Rotational Stabilization of Cargo Container Slung Loads

Abstract

The stabilization of “difficult” loads that become aerodynamically unstable at airspeeds well below the power-limited speed of the helicopter-load configuration has been studied since the 1960s. This paper looks at the possibility of stabilizing slung loads in forward flight by imposing a slow steady rotation in yaw (spin stabilization). Slow rotations of 100–150 deg/s suffice to suppress the pendulum motions of the load. A swivel is required at the hook, and only a few foot-pounds of yaw moment are needed to overcome swivel friction and impose the desired yaw rate. The approach is limited to single-point suspensions. A stabilizer design consisting of a one-shaft anemometer-like device with hemispherical cups at the ends was developed in wind tunnel tests. The shaft angle can be controlled to vary the applied yaw moment and allow feedback regulation of the load yaw rate. Flight tests with two cargo containers demonstrated that a simple linear control law with fixed gains was effective in maintaining the desired yaw rate in forward flight over the range of configurations of the test loads. Wind tunnel data were obtained at all stages of the development and testing and proved to be an accurate source of design data and an accurate predictor of performance in flight.

Stabilization control for unmanned helicopter-slung load system based on active disturbance rejection control and improved sliding mode control

“…We can obtain _ u in (7) from (5). And it can also be written in (8). AI T 1 and Λ T represent 6n À c and c rows of…”

“…There were many researches to stabilize the helicopter/ load system ranging from passive to active control. The passive stabilization method focused on placing an active arm 4 , fins [5][6][7] or anemometric cup 8 on the underslung load to achieve stabilization. For certain underslung loads, the trimmed flight speed could be increased from 60 kts-110 kts using a certain size fin.…”

“…6 And an anemometric cup designed for rotational stabilization could extend the helicopter/system's flight envelope from 60 kts to approximately 120 kts. 8 But this method had many difficulties.…”

Testing-Based Approach to Determining the Divergence Speed of Slung Loads

“…These data have been successfully matched by simulations from the authors' research group, as discussed later. Another flight dataset is available on a ribbon bridge model [16].…”

“…This has led to a large volume of work, which we can only touch here by referring to recent work. Passive stabilization continues to be studied using rotation of CONEX containers, as used by Cicolani [16]. Their group has also studied active stabilization using deployable vanes attached to one side of the container.…”